Process for preparing hydrazodicarbonamide via ketimines

ABSTRACT

The present invention relates to a novel process for preparing hydrazodicarbonamide (HDC) that is, after oxidation to azodicarbonamide (ADC), used industrially as a polymer auxiliary.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a novel process for preparinghydrazodicarbonamide (“HDC”) which is, after oxidation toazodicarbon-amide (“ADC”), used as a polymerization auxiliary (Ullmann'sEncyclopaedia of Industrial Chemistry, Vol. A13, 185).

[0002] It is generally known that HDC is obtained from the reaction ofhydrazine with urea (Ullmann's Encyclopaedia of Industrial Chemistry,Vol. A13, 185). The yields in this process are good. However, hydrazineis relatively expensive since it is prepared by chlorination of ammoniaand is also classified as a hazardous substance.

[0003] It is also known that hydrazine can be obtained from the reactionof ammonia and hydrogen peroxide in the presence of ketones andcatalysts. However, the yields leave something to be desired. (Ullmann'sEncyclopaedia of Industrial Chemistry, Vol. A13, 182).

[0004] Furthermore, it is known that benzophenonimine can be oxidizedusing oxygen in the presence of catalysts to give benzophenonazine,however, which can be cleaved only with strong acids such as sulfuricacid to form hydrazinium sulfate (Catal. Rev. CR Sci. Eng., 1990, 32,229-277). The direct reaction of this benzophenonazine with urea to formHDC is, however, not successful.

SUMMARY OF THE INVENTION

[0005] It has now been found that hydrazodicarbonamide (“HDC”) offormula (I)

[0006] can be prepared by a process comprising

[0007] (a) reacting aliphatic ketones of formula (II)

[0008] wherein

[0009] R¹, R², and R³ are identical or different and are eachsubstituted or unsubstituted alkyl, and

[0010] R⁴ is hydrogen, substituted or unsubstituted alkyl, orsubstituted or unsubstituted cycloalkyl, or

[0011] R¹ together with R² or R⁴ form an alkylene chain, with ammoniaunder pressure to form ketimines of formula (III)

[0012] wherein

[0013] R¹, R², R³ and R⁴ are as defined above,

[0014] (b) oxidizing the ketimines of formula (III) with oxygen in thepresence of catalysts to form ketazines of formula (IV)

[0015] wherein

[0016] R¹, R², R³ and R⁴ are as defined above, and

[0017] (c) reacting the ketazines of formula (IV) with urea and water inthe presence of catalysts.

BRIEF DESCRIPTION OF THE DRAWING

[0018] Scheme 1 illustrates an embodiment of the invention using3,3-dimethyl-2-butanone (pinacolone) as starting ketone.

DETAILED DESCRIPTION OF THE INVENTION

[0019] It is extremely surprising that aliphatic ketimines of formula(III) are formed with high selectivity and can be oxidized with highselectivity using oxygen to form ketazines of formula (IV). It islikewise surprising that the ketazines of formula (IV) can be reacteddirectly with urea and water to give hydrazodicarbonamide (I).

[0020] The process of the invention has a series of advantages. Thus,the use of hydrazine can be avoided, oxygen is used in place of chlorineas oxidant, and the ketone is set free in the last step and can bereturned to the cyclic process. The net reaction of the cyclic processis the oxidation of urea using oxygen to give hydrazodicarbonamide andwater.

[0021] If 3,3-dimethyl-2-butanone (i.e., pinacolone) is used as startingketone, the cyclic process according to the invention can be illustratedby Scheme 1.

[0022] The ketones used for carrying out the process of the inventionare defined in general terms by the formula (II). Preference is given tocompounds of formula (II) in which

[0023] R¹, R², and R³ are identical or different and are eachstraight-chain or branched alkyl having from 1 to 6 carbon atoms,

[0024] R⁴ is hydrogen, straight-chain or branched alkyl having from 1 to6 carbon atoms, or cycloalkyl having from 3 to 6 carbon atoms, wherethese radicals may bear one or two identical or different substituentsselected from among halogen, alkoxy having from 1 to 4 carbon atoms, andcycloalkyl having from 3 to 6 carbon atoms,

[0025] or

[0026] R¹ together with R² or R⁴ form an alkylene chain having from 2 to6 carbon atoms, where this chain may bear from 1 to 4 identical ordifferent substituents selected from among halogen, alkyl having from 1to 4 carbon atoms, and cycloalkyl having from 3 to 6 carbon atoms.Particular preference is given to using as starting materials ketones

[0027] of formula (II) in which

[0028] R¹, R², and R³ are identical or different and are each methyl orethyl, and

[0029] R⁴ is hydrogen, methyl, ethyl, isopropyl, or tert-butyl,

[0030] or

[0031] R¹ and R² together form an alkylene chain having 4 or 5 carbonatoms,

[0032] or

[0033] R¹ and R⁴ together form an alkylene chain having 3 or 4 carbonatoms.

[0034] The ketones of formula (II) are known or can be prepared by knownmethods.

[0035] Step (a) of the process of the invention is carried out usingammonia under a pressure (either its own pressure or inert gas pressure)of from 20 to 300 hectopascals, preferably from 50 to 200 hectopascals.Ammonia is used in a molar ratio to the ketone of from 1:1 to 20:1,preferably from 2:1 to 10:1. In addition, a catalyst, preferablyammonium salts such as ammonium chloride or ammonium sulfate, can beused if desired.

[0036] Suitable diluents are all inert solvents. Preference is given tocarrying out the reaction without diluents.

[0037] The reaction temperatures when carrying out step (a) can bevaried within a certain range. In general, temperatures of from 0° C. to200° C. (preferably from 20° C. to 120° C.) are employed.

[0038] Since the ketimine of formula (III) that is obtainable asintermediate is readily hydrolyzed, the reaction mixture is cooled totemperatures of from 20° C. to −78° C. (preferably from 0° C. to-30° C.)before depressurization. The organic phase is separated from the aqueousphase and can be purified after drying. The mixture of ketimine offormula (III) and the starting material of formula (II) isadvantageously used directly in the reaction step (b) without furtherpurification.

[0039] The ketimine of formula (III) is used in reaction step (b) eitherin pure form or in admixture with the ketone of formula (II). Oxygen canbe used in pure form or diluted with inert gases such as nitrogen,preferably as air, under atmospheric pressure or under a pressure of upto 20 hectopascals.

[0040] Suitable catalysts are salts of the metals Cr, Mn, Fe, Co, Ni,TI, Pb, Cu, or Ag, preferably their halides, particularly preferablycopper derivatives such as CuCl or CuBr. The catalysts can be usedalone, in aqueous solution, in mixtures of various metal salts, orapplied to a support. In general, the catalyst is used in amounts offrom 0.01 to 30% by weight, preferably from 0.05 to 20% by weight.

[0041] Suitable diluents are all inert solvents. Unreacted ketone offormula (II) from reaction step (b) is preferably employed.

[0042] The reaction temperatures when carrying out step (b) can bevaried within a certain range. In general, temperatures of from 0° C. to100° C. (preferably from 20° C. to 80° C.) are employed.

[0043] To bind the water formed in the oxidation, it is advantageous touse a desiccant such as zeolite or sodium sulfate.

[0044] For the work-up, the organic phase is separated from the aqueouscatalyst phase and purified by distillation. The isolated ketone offormula (II) is returned to the circuit, the catalyst solution islikewise reused directly or after work-up and the ketimine of formula(IV) is used in step (c).

[0045] In reaction step (c) of the process of the invention, theketazine of formula (IV) is reacted with urea and water in the presenceof a catalyst. Ketazine and urea are used in a molar ratio of from 1:2to 1:5, preferably from 1:2 to 1:3. Water is used as solvent in anequimolar amount or in a large excess.

[0046] Suitable catalysts are mineral acids such as sulfuric acid orphosphoric acid, organic acids such as trifluoroacetic acid ortrifluoromethanesulfonic acid, or acid salts such as ammonia sulfate orammonium chloride. These catalysts can be used in catalytic amounts of0.1% by weight and more or in a large excess.

[0047] Suitable diluents are polar solvents such as dimethylformamide(“DMF”), acetic acid, water, or mixtures thereof.

[0048] The reaction temperatures when carrying out step (c) can bevaried within a certain range. In general, temperatures of from 80° C.to 150° C. (preferably from 100° C. to 130° C.) are employed.

[0049] The reaction can be carried out at atmospheric pressure or underpressure, with the removal of the ammonia liberated having to beensured.

[0050] The reaction product hydrazodicarbonamide of formula (I) can beisolated from the reaction solution as a solid product by filtrationwith suction. The ketone of formula (II) that is set free is isolatedfrom the reaction solution by distillation and returned to the cyclicprocess.

[0051] The following examples further illustrate details for the processof this invention. The invention, which is set forth in the foregoingdisclosure, is not to be limited either in spirit or scope by theseexamples. Those skilled in the art will readily understand that knownvariations of the conditions of the following procedures can be used.Unless otherwise noted, all temperatures are degrees Celsius and allpercentages are percentages by weight.

EXAMPLES

[0052] Preparative Example

[0053] a) Pinacolonimine: 50 g (0.5 mol) of 3,3-dimethyl-2-butanone(pinacolone) and 0.5 g of ammonium chloride were placed in a 0.3 literautoclave, 100 ml (4 mol) of liquid ammonia were subsequently added, andthe mixture was heated to 80° C. The pressure was increased to 200 barusing nitrogen. The mixture was then stirred for 2 hours at 80° C. Afterthe reaction was cooled to 0° C., the pressure was slowly released. Thereaction mixture was poured into a separating funnel and the phases areseparated.

[0054] Aqueous phase (bottom, having a high NH₃ content): 5.77 g

[0055] Organic phase (top): 49.29 g (0.3 mol, 60% imine); GC: 37.0%ketone and 62.6% pinacolonimine; ¹H—NMR (CDCl₃, 400 MHz): δ 8 1.15 (9H,s); 2.03 (3H, s);˜9.0 (NH); GC/MS(CI): 100 (M+H⁺)

[0056] b) Pinacolonazine: 5.0 g of a mixture of pinacolonimine (24.6%,12.4 mmol) in 3,3-dimethyl-2-butanone (pinacolone) together with 0.2 gof copper(I) chloride and 2.0 g of Zeolith 134® were placed in areaction vessel at room temperature. While passing air over the mixtureand stirring, the mixture was subsequently heated at 40° C. for 5 hours.After cooling, the reaction mixture was diluted with dichloromethane andshaken with dilute ammonia solution. The organic phase was dried oversodium sulfate, filtered, and evaporated under reduced pressure to give1.0 g (4.7 mmol, 76% of theory) of pinacolonazine having a GC content of93.4% and 2.5% of pinacolone.

[0057]¹H—NMR (CDCl₃, 400 MHz): δ 1.17 (18H, s); 1.68 (6H, s); GC/MS(EI):196 (M⁺).

[0058] c) Hydrazodicarbonamide (HDC): 6.2 g of ammonium sulfate wereadded to a mixture of 1.96 g (10 mmol) of pinacolonazine with 3.6 g (60mmol) of urea in 5 ml of water and 5 ml of DMF and the reaction mixturewas heated at reflux over the weekend (72 h). The product thatprecipitated was filtered off with suction, washed with water, and driedunder reduced pressure to give 1.0 g (8.5 mmol, 85%) of HDC having amelting point of 254° (decomposition).

What is claimed is:
 1. A process for preparing hydrazodicarbonamide offormula (I)

comprising (a) reacting an aliphatic ketone of formula (II)

wherein R¹, R², and R³ are identical or different and are eachsubstituted or unsubstituted alkyl, and R⁴ is hydrogen, substituted orunsubstituted alkyl, or substituted or unsubstituted cycloalkyl, or R¹together with R² or R⁴ form an alkylene chain, with ammonia underpressure to form a ketimine of formula (III)

wherein R¹, R², R³ and R⁴ are as defined above, (b) oxidizing theketimine of formula (III) with oxygen in the presence of a catalyst toform a ketazine of formula (IV)

wherein R¹, R², R³ and R⁴ are as defined above, and (c) reacting theketazine of formula (IV) with urea and water in the presence of acatalyst.
 2. A process according to claim 1 wherein, in the compound offormula (II), R¹, R², and R³ are identical or different and are eachstraight-chain or branched alkyl having from 1 to 6 carbon atoms, R⁴ ishydrogen, straight-chain or branched alkyl having from 1 to 6 carbonatoms, or cycloalkyl having from 3 to 6 carbon atoms, where theseradicals optionally bear one or two identical or different substituentsselected from among halogen, alkoxy having from 1 to 4 carbon atoms, andcycloalkyl having from 3 to 6 carbon atoms, or R¹ together with R² or R⁴form an alkylene chain having from 2 to 6 carbon atoms, where this chainoptionally bear from 1 to 4 identical or different substituents selectedfrom among halogen, alkyl having from 1 to 4 carbon atoms, andcycloalkyl having from 3 to 6 carbon atoms.
 3. A process according toclaim 1 wherein in step (a) ammonia is used under a pressure of from 20to 300 hectopascals and the reaction temperature is from 0° C. to 200°C.
 4. A process according to claim 1 wherein the reaction mixture iscooled to temperatures of from 20° C. to −78° C. beforedepressurization.
 5. A process according to claim 1 wherein in reactionstep (b) oxygen is used in pure form or is diluted with an inert gas atatmospheric pressure or under a pressure of up to 20 hectopascals.
 6. Aprocess according to claim 1 wherein a salt of Cr, Mn, Fe, Co, Ni, TI,Pb, Cu, or Ag is used as catalyst.
 7. A process according to claim 1wherein the reaction temperature in step (b) is from 0° C. to 100° C. 8.A process according to claim 1 wherein in step (c) the molar ratio ofthe ketazine of formula (IV) to urea is from 1:2 to 1:5.
 9. A processaccording to claim 1 wherein in step (c) the catalyst is used in amountsof at least 0.1% by weight or in a large excess.
 10. A process accordingto claim 1 wherein the reaction temperature in step (c) is from 80° C.to 150° C.